<!DOCTYPE html>
<html lang='en'>

<head>
    <meta charset='UTF-8'>
    <meta http-equiv='X-UA-Compatible' content='IE=edge'>
    <meta name='viewport' content='width=device-width, initial-scale=1.0'>
    <title>Document</title>
    <script src='../vue.global.js'></script>
</head>

<body>
    <div id='app'></div>
    <script>
        const app = Vue.createApp({
            data() {
                return { count: 4 }
            }
        })

        const vm = app.mount('#app')

        console.log(vm.$data.count) // => 4
        console.log(vm.count)       // => 4

        // 修改 vm.count 的值也会更新 $data.count
        vm.count = 5
        console.log(vm.$data.count) // => 5

        // 反之亦然
        vm.$data.count = 6
        console.log(vm.count) // => 6
    </script>
</body>

</html>